Electrocoating compositions are well known and are disclosed in Gilchrist patents, such as U.S. Pat. Nos. 3,351,675, 3,362,899, 3,575,909, and 3,351,575, and the same are incorporated herein by reference. Prior art electrocoating compositions are often cured by the inclusion of catalysts which cure the electrocoated composition by application of heat. Electrodeposition of conventionally heat-curable electrocoating polymers onto cathode substrates are disclosed in U.S. Pat. Nos. 3,617,458 and 3,679,564, and said patents are incorporated herein by reference. More recently, electron beam polymerization of electrocoating compositions has been suggested in U.S. Pat. No. 3,501,390 and U.S. Pat. No. 3,501,391, and the same are incorporated herein by reference.
It now has been found that a water-dispersible ethylenically unsaturated polymer containing ultraviolet sensitizer can be solubilized in aqueous solutions for use in electrocoating baths. The polymer can be uniformly electrocoated onto a cathode substrate while maintaining a critical ratio of ultraviolet sensitizer to polymer whereby consistent and uniformly cured paint films can be achieved upon exposure to ultraviolet (UV) energy. This invention provides an expedient and efficient solution to inherent problems in electrocoating a polymer onto a cathode substrate wherein the polymer tends to electrocoat at a different rate than the sensitizer. In this regard, electrocoating polymers must be rendered water soluble as well as curable by ultraviolet energy. Electrocoating compositions of this invention contain the ultraviolet sensitizers wherein the polymer and sensitizer are stabilized in the electrocoating bath to properly maintain a constant ratio of sensitizer to polymer when the polymer is electrocoated onto the cathode substrate. Up to about 5% photosensitizer is required to activate the polymer with actinic radiation and the ratio of polymer relative to a low percentage of ultraviolet sensitizer must be maintained upon electrocoating the polymer onto the cathode substrate so that a complete cure is achieved upon exposure to ultraviolet light.
Accordingly, a primary object of this invention is to provide an electrodepositable composition containing a stabilized ratio of ultraviolet sensitizer dispersed in an ethylenically unsaturated polymer solubilized in aqueous solution that can be efficiently and uniformly electrocoated onto a cathode substrate and subsequently cured with ultraviolet energy.
A further object is to provide a water dispersed polymer containing ultraviolet sensitizer connected to the polymer backbone and suitable for electrocoating on a cathode substrate and curable by ultraviolet sensitizer.
A further object is to provide a process for solubilizing an ethylenically unsaturated polymer containing an ultraviolet sensitizer within a aqueous solution, electrocoating a constant ratio of ultraviolet sensitizer and polymer onto a cathode conductive substrate to provide a paint film, and irradiating the coating with ultraviolet energy until the paint film becomes fully cured.
These and other advantages of the invention will become more apparent by referring to the Detailed Description of the Invention.